Parkinson's Drug Reduces Fibromyalgia Pain

Action Points

Inform patients that in this small, short duration study, Mirapex was associated with a greater degree of pain relief than placebo.

Understand that Mirapex is approved by the FDA only for the treatment of idiopathic Parkinson's disease.

Be aware that in this study, subjects were allowed to continue on their existing medications, which could have altered the results.

Be aware that the lead author of the study holds patents on the use of this category of medication in the treatment of fibromyalgia.

RENTON, Wash. July 28-The Parkinson's disease drug Mirapex (pramipexole) reduced pain and fatigue and improved function in some patients with fibromyalgia in a small study, reported investigators in a private rheumatology practice here.

In a randomized trial comparing Mirapex with placebo in 49 patients with fibromyalgia, patients who received Mirapex experienced gradual and more significant improvements in measures of pain, fatigue, function, and global status than patients on placebo, according to Andrew J. Holman, M.D., and Robin R. Myers, M.S., of Pacific Rheumatology Associates here.

Their findings were published in the August issue of Arthritis & Rheumatism.

Recent research suggests that pain associated with fibromyalgia may be caused by abnormal sensory processing in the central nervous system. Mirapex, a dopamine receptor agonist with particular affinity for the dopamine3 receptor agonist, could theoretically mitigate symptoms of fibromyalgia through its effects on dopamine stimulation.

Dr. Holman holds a U.S. patent for the use of dopamine2 and dopamine3 receptor agonists in the treatment of fibromyalgia. Mirapex is indicated by the FDA only for treatment of idiopathic Parkinson's disease.

Based on observations of Mirapex's efficacy in treating fibromyalgia in open-label studies, and for the treatment of restless leg syndrome (which is more common in patients with fibromyalgia than in healthy controls) in placebo-controlled trials, the investigators designed the randomized study.

In this placebo-controlled, parallel group, dose-escalation trial, 60 patients were randomly assigned on a 2:1 basis to either Mirapex or placebo, respectively. Patients given the active drug were started at a dose of 0.25 mg at bedtime the first week, with the dose increasing by 0.25 mg/day weekly, to a maximum dose of 4.5 mg/day at weeks 12, 13 and 14. The dose was then tapered to 0 over week 15. Evaluations were conducted every two weeks, with the final evaluation at week 15.

Participants who were on a stable dose of concomitant medications such as analgesics for at least six weeks prior to study entry were allowed to continue on those medications during the study, but patients who started new medications during the study period were dropped. In all, 49 of 60 patients completed the study, which included an intent-to-treat analysis.

Both placebo-treated and Mirapex-treated patients reported significant decreases in pain, but the decrease was significantly greater among patients treated with the active drug. At 14 weeks the decrease in pain as measured by the pain score on the visual analog scale (VAS) was 36% among Mirapex-treated patients, and 9% among those on placebo. In the active drug group, 42% reported a decrease in pain of at least 50%, compared with 14% of the placebo group.

Mirapex also appeared to have the edge over placebo in secondary measures of efficacy, including the Fibromyalgia Impact Questionnaire score, pain improvement scale, Multidimensional Health Assessment Questionnaire, VAS fatigue, and VAS global scores.

The most common adverse events in patients taking Mirapex were weight loss and nausea; patients on placebo also reported nausea, possibly due to the influence of potentially suggestive language on the consent form, the authors speculated.

Patients taking Mirapex did not report hallucinations or sleep attacks that are commonly seen in those taking the drug for Parkinson's disease.

The authors acknowledged that the study results are limited by the concomitant use of other medications and by the short duration.

"Finally, it should be noted that some exclusion criteria in this study were particularly important," the authors wrote. "Both positional cervical myelopathy and untreated obstructive sleep apnea are potent adrenergic arousals that commonly contribute to autonomic dysregulation. Both conditions limit the efficacy and tolerability of a D3 agonist when used to treat fibromyalgia. Given the significant prevalence of cervical pain and obstructive sleep apnea in patients with fibromyalgia, many may not respond to treatment with pramipexole."

Reviewed by Robert Jasmer, MD Assistant Professor of Medicine, University of California, San Francisco